Ewa Bidzińska

EPR spectroscopy as a tool for investigation of differences in radical status in wheat plants of various tolerances to osmotic stress induced by NaCl and PEG-treatment.

Two kinds of wheat genotypes with different tolerance to osmotic stress (NaCl and PEG-treatment) were investigated with biochemical analyses, including the measurements of total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, reducing power and starch content. The results were compared with electron paramagnetic resonance (EPR) data concerning the nature and amounts of stable long lived radicals present in the control and stressed plants. In addition, the changes in manganese content upon stress conditions were monitored. Different mechanisms of protection against PEG stress in sensitive and tolerant wheat genotypes were postulated. In sensitive genotypes, electrons were created in excess in stress conditions, and were stabilized by polysaccharide molecules, whereas in tolerant genotypes, protection by antioxidants dominated. Moreover, the quinone-semiquinone balance shifted towards semiquinone, which became the place of electron trapping. NaCl-treatment yielded significant effects mainly in sensitive genotypes and was connected with the changes of water structure, leading to inactivation of reactive oxygen species by water molecules.

Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.

Interactions of chromium ions with starch granules in an aqueous environment.

In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.

Effect of Sweeteners on Radical Formation in Starch Studied by Electron Paramagnetic Resonance Spectroscopy

The process of radical generation occurring upon thermal treatment of potato and corn starch containing sweeteners: saccharose, acesulfam K, aspartame, and sorbitol was investigated by electron paramagnetic resonance spectroscopy, using Cu2+ ions as a paramagnetic probe. It was found that the influence of acesulfam K and sorbitol on radical formation is stronger than that of other additives. Acesulfam K increased the amount of radicals in the starch compared to native starch, whereas sorbitol significantly decreased their concentration. The influence of sweeteners on radical processes in the starch is because of differences in their molecular structures and presence or absence of OH groups.

Silver–Alumina Catalysts for Low-Temperature Methanol Incineration

The use of methanol as an alternative fuel for gasoline or diesel engines increases the unregulated CH3OH emission. γ-Al2O3 modified with Cu, Mn, Ce, K, Ag, Cu–Mn, Cu–Ce, Cu–Ag or Cu–K (0.5, 1.0, 0.5:0.5, 1.0:1.0 wt% of metal) catalysed the process of methanol incineration. The highest activity reached samples containing 1.0 wt% of silver. Dispersed Ag+ species on Al2O3 served as active species for selective oxidation of CH3OH to CO2 over both Ag/Al2O3 and Cu–Ag/Al2O3. Additionally, the XPS and EPR results revealed the AgO interface between the Ag2O and CuO in the Cu–Ag system.Graphical Abstract

Optical nonlinearity and electric conductivity origin study on sucrose crystal by using IR, Raman, INS, NMR, and EPR spectroscopies.

The supposed importance of hydrogen bonds toward the origin of second harmonic generation (SHG) and electric conductivity in crystalline sucrose was investigated by IR (4000-10cm(-1)), INS (2000-10cm(-1), at 35K), polarized Raman (3600-50cm(-1)) spectra, and (1)H NMR second moment line records in the temperature range 450-80K. The temperature dependence of NIR (7000-5500cm(-1)) polarized spectra gave information about -CH2 motions complementary to NMR results concerning -CH2OH group rearrangements. The EPR spectra were applied to study the generation of radical ions by exposure to NIR radiation. Density functional theory quantum chemical calculations were performed to reproduce the vibrational spectra in order to complete as far as possible the assignments of bands observed by us and in the literature in sucrose crystals, and to throw more light on the possible reasons of sucrose electric conductivity and optical nonlinearity by the knowledge of theoretical values of dipole moments, polarizabilities, first order hyperpolarizabilities of sucrose molecule and clusters as well as ionization energy and electron affinity. The proton transfer in one specific hydrogen bond parallel to the helical axis b is proposed to be the most important in SHG and conductivity origin.

Tpr, EPR and UV-Vis studies of Ni(II) speciation in chrysoprase

TPR (Temperature Programmed Reduction) and EPR (Electron Paramagnetic Resonance) corroborated with UV-Vis methods were used to get a new insight into the status of nickel ions in chrysoprases from various localities. The investigation showed speciation of Ni into 2 : 1 highly dispersed phyllosilicates and extra-framework species grafted on the surface of chalcedony matrix. Both kinds of nickel exhibit a distorted octahedral coordination giving rise to a broad EPR spectrum with g = 2.17 and three characteristic d-d bands that can be parameterised with 10Dq = 8897cm - 1 and B = 953 cm - 1 .

Effect of thermal treatment on potato starch evidenced by EPR, XRD and molecular weight distribution.

Effect of heating of the potato starch on damages of its structure was investigated by quantitative electron paramagnetic resonance (EPR) spectroscopy, X‐ray diffraction and determination of the molecular weight distribution. The measurements were performed in the temperature range commonly used for starch modifications optimizing properties important for industrial applications. Upon thermal treatment, because of breaking of the polymer chains, diminishing of the average molecular weights occurred, which significantly influences generation of radicals, evidenced by EPR. For the relatively mild conditions, with heating parameters not exceeding temperature 230 °C and time of heating equal to 30 min a moderate changes of both the number of thermally generated radicals and the mean molecular weight of the starch were observed. After more drastic thermal treatment (e.g. 2 h at 230 °C), a rapid increase in the radical amount occurred, which was accompanied by significant reduction of the starch molecular size and crystallinity. Experimentally established threshold values of heating parameters should not be exceeded in order to avoid excessive damages of the starch structure accompanied by the formation of the redundant amount of radicals. This requirement is important for industrial applications, because significant destruction of the starch matrix might annihilate the positive influence of the previously performed intentional starch modification. Copyright

Thermally generated radicals as indicators of the starch modification studied by EPR spectroscopy: a review.

The results compiled and discussed in the present review have been published by the research group of the Chemistry Faculty, Jagiellonian University or by other Authors, as given in References. Relatively stable and short-lived radicals generated thermally in starches of various botanic origin were used as indicators of the changes in the starch structure and properties occurring upon chemical and physical modifications. The number of radicals was determined by electron paramagnetic resonance (EPR) spectroscopy. Distribution of water and accessibility of different zones in the starch granule for reagents were tested by using paramagnetic Cu(2+) ions as a probe molecule. Relatively stable radicals generated in starch at 300°C revealed protective properties against ionizing radiation. Thermally induced short-lived radicals exhibited sensitivity to the degree of the starch structure ordering.

Effects of Saccharose Substitutes on Physicochemical Properties and Free Radical Generation in Oxidized Potato Starch

This study aimed at investigating the effects of saccharose and its substitutes (sorbitol, acesulphame, aspartame) added to potato starch oxidized with sodium chlorate (I) on the physicochemical properties of starch and generation of free radicals at both 150 and 230°C. Oxidized starch with saccharose and its substitutes were analyzed by thermodynamic characterization of pasting, rheological properties, and susceptibility to degradation of 2% pastes. Moreover, a number of generated thermally free radicals in investigated samples was determined by quantitative electron paramagnetic resonance spectroscopy measurements. Saccharose and sorbitol increased considerably the onset temperature of transition (T0) and the peak temperature of transistion (Tp) as determined by differential scanning calorimetry. Among the sweeteners, only aspartame influenced the characteristic viscosities of the starch-sweetener-water systems, reducing the thermal stability of the obtained pastes. Acesulphame K and aspartame caused the largest increase in the susceptibility to retrogradation of 2% pastes of oxidized potato starch. In the presence of sorbitol, the number of radicals generated thermally in starch decreased. This effect, found by quantitative electron paramagnetic resonance spectroscopy measurements, indicates effective interaction of hydroxyl groups of the sorbitol molecule with starch matrix, leading to the stabilization of the starch structure.